This invention relates generally to a variable geometry nozzle to be used on an augmented turbofan engine, and, more particularly to a liner assembly which effectively protects the flaps and seals of the nozzle from the large thermal gradients established between the hot inner surface of the nozzle and cooled supporting member.
With the increasing interest in power plants for high Mach supersonic flight, e.g., turbo-ramjets, pure ramjets and rockets, it has become increasingly important to provide means for optimizing engine operating efficiency under dissimilar flight conditions. For example, it is known that for subsonic operation an efficient type of jet exhaust nozzle is a nozzle having a convergent shape. However, as near sonic and at supersonic speeds it is more desirable to employ a nozzle having a convergent portion followed by a divergent portion. For most efficient operation it is also desirable to provide means to vary both the minimum flow area, or throat, of the convergent portion of the nozzle and the nozzle exit area at the downstream end of the divergent portion.
In order to fulfill the requirements set forth hereinabove it has become accepted practice to provide what is commonly known as the "variable area convergent-divergent nozzle." Examples of such a nozzle may be found in U.S. Pat. Nos. 3,044,258 and 3,214,905.
It is also desirable, due to the high temperatures associated with the use of the nozzle set forth hereinabove to provide some means for cooling the interior of the nozzle. Since, as discussed hereinabove, such a nozzle should be infinitely adjustable over a wide range of operating conditions, the means for cooling, i.e., providing secondary air flow, should be controlled or scheduled so that a continuous and, at all times, sufficient air flow is provided. U.S. Pat. Nos. 3,972,475 and 3,979,065 provide illustrations of variable area convergent-divergent nozzles which incorporate therein acceptable cooling means.
Unfortunately, however, the advent of cooled variable area convergent-divergent nozzles has also produced particular problems with respect to the individual parts which make up the nozzle. Nozzles heretofore in use had problems with respect to durability of parts, in that, sections of the nozzle quite readily distorted, cracked and even burned away in a period of time much shorter than called for by the design parameters.
This durability problem has been especially troublesome in designs where large thermal gradients were induced in the flap and seal liners. These gradients were due to simultaneous exposure of the flap and seal liners to the hot exhaust gases and the cooling air. The problem was further aggravated by (1) part configuration, (2) cooling air leakage, (3) vibration, and (4) hot gas inflow. As a result thereof, thermal stresses quickly distorted the parts. In a short time, for example, cracks occurred which produced leakage of the hot gas, which in turn quickly burned away the heat sensitive underlying parts, thereby destroying the nozzle. Furthermore, in many instances, cooling air in the convergent-divergent nozzle could not be properly controlled to protect the divergent portion thereof. As a consequence, that portion of the nozzle was burned away, thereby destroying the nozzle.
In general, the flaps of an exhaust nozzle are made of Titanium (Ti). Titanium in an excellent lightweight structural metal, until, unfortunately it gets hot. Means must, therefore, be provided to protect the Titanium flaps from the hot exhaust gases.
Prior art thermal protection of Titanium flaps is accomplished using Colombium (Cb) liners. Unfortunately, Colombium is heavy, very costly and of sufficient rarity so as to possibly not be readily available in the future. It is therefore essential to replace completely any and all need for the element Colombium in engine exhaust nozzles. Furthermore, in so doing it is also readily apparent that the relative cool air flowing over and near the Ti flaps must be separated from the wiltingly hot exhaust gases from the combustion section of the engine, thereby protecting the flaps.